1. Field of the Invention
The present invention relates to a zooming optical system and an electronic image pickup apparatus using the same.
2. Description of the Related Art
A digital camera has reached a level of being used practically, regarding making large the number of pixels (high image quality), and small-sizing and slimming. From a function point of view and a market point of view, a digital camera has substituted a silver salt 35 mm film camera. Therefore, as a next trend of evolution, further increase in the number of pixels along with a high zooming ratio and widening of an angle with the same size and slimness has been sought strongly. As a zooming optical system in which, slimming of an optical system has been realized, an optical system in which, a reflecting optical element for folding an optical path (a zoom lens of a folding type) is used in a first lens group (first lens group from an object side), has hitherto been available. When such zooming optical system is used, it is possible to make a depth of a camera casing extremely slim.
In the zoom lens system of the folding type, the reflecting optical element is disposed in the first lens group, and a path of a light beam is folded by the reflecting optical element. Here, in a case of folding assuredly the path of a light beam having an angle of field of a certain extent, it is necessary to secure a reflecting surface of a width required for folding in the reflecting optical element. Therefore, in the first lens group, an air conversion thickness along an optical axis increases inevitably. Particularly, when the angle is widened, the increase in the air conversion thickness becomes remarkable.
Therefore, in such optical system, by disposing a negative refracting power immediately before a reflecting surface and a positive refracting power immediately after the reflecting surface a width of the reflecting surface is made small, and the air conversion thickness is also made thin to some extent. As an example of an optical system with a high zooming ratio having such structure, optical systems disclosed in Japanese Patent Application Laid-open Publication No. 2005-195757 and 2008-129238 are available.